In the course of completing an oil and/or gas well, it is common practice to run a string of protective casing or liner into the well bore and then to run production tubing inside the casing. The annulus between the liner or casing and the surrounding formation is sealed with a deposit of cement to prevent fluid flow through the external annulus from one formation zone to another. The cement is pumped through a work string suspended within the casing or liner into the annular space between the liner or casing and the surrounding well bore.
If the lining or casing traverses a hydrocarbon-bearing formation, the lining is perforated to create flow apertures through the casing and cement so that the formation fluids can flow into the well. The liner and/or well casing is perforated by a perforating gun which is suspended within the well. Shaped explosive charges carried by the gun blast openings through the metal lining, the cement deposit and the surrounding formation.